This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application entitled FUSING ROLLER OF ELECTROPHOTOGRAPHIC IMAGE FORMING APPARATUS filed with the Korean Industrial Property Office on Nov. 16, 2001 and there duly assigned Serial No. 2001-0071399.
1. Field of the Invention
The present invention relates to a fusing roller in an electrophotographic image forming apparatus, and more particularly, to a design for a fusing roller used in an electrophotographic image forming apparatus that minimizes a surface temperature gradients over the surface of the fusing roller.
2. Description of the Related Art
Designs of fusing roller units adopting a heat pipe capable of instantaneously heating the fusing roller due to high heat conductivity an having low power consumption are disclosed in Japanese Patent Publication Nos. Hei 5-135656, Hei 10-84137, Hei 6-29663, and Hei 10-208635. Such fusing roller units adopting the heat pipe have a structure in which heat sources having different shapes are provided at one side end of the fusing roller unit deviating from a fusing region. In the arrangement structure of heat sources, the overall length of the fusing roller unit may be enlarged, and thus structural complication should be improved.
Also, the fusing roller units disclosed in Japanese Patent Publication Nos. Sho 58-163836, Hei 3-107438, Hei 3-136478, Hei 6-316435, Hei 7-65878, and Hei 7-105780, and Hei 7-244029 have a structure in which heat sources are provided inside the fusing rollers, and thus the above-mentioned enlargement of the overall length does not occur. However, the fusing roller units have a plurality of partial heat pipes, and thus processing and manufacturing of the fusing roller units are very complicated.
Further, the heat pipes are arranged partially in the fusing roller units, and thus a temperature difference between a portion among the heat pipes and a portion contacting the heat pipes occurs. When a temperature difference occurs in the fusing roller, ink such as toner, is not properly transferred onto the paper, degrading printing quality.
Serial Nos. 60/257,118, 09/947,657 and 09/967,934 teach a fusing roller that has a resistive heating element wound about the fusing roller in a spiral fashion. Near the axis of the fusing roller is a heat pipe comprising a working fluid and a wick. Although this design of a fusing roller enables the fusing roller to be heated quickly, the surface of the fusing roller has an unwanted temperature gradient along the length of the fusing roller. When recently heated, the center portion of the fusing roller is at a higher temperature than the surface of the fusing roller near the ends of the fusing roller.
What is needed is a design for a fusing roller that eliminates these temporary temperature gradients along the length of the surface of the fusing roller by compensating for the temperature gradients along the length of the surface of the fusing roller.
It is therefore an object of the present invention to provide a design for a fusing roller used in an electrophotographic image forming apparatus, the fusing roller including a heating portion having an improved structure in which the above-referenced surface temperature gradients of the fusing roller can be minimized, and thus a high quality fusing of the toner image can be achieved with minimal warm up times.
To achieve the above object, according to one aspect of the present invention, there is provided a novel design for a fusing roller used in an electrophotographic image forming apparatus. The fusing roller includes an internal pipe having enclosed both ends in which a vacuum state of predetermined pressure is maintained and a predetermined amount of working fluid is stored, a fusing portion installed to surround the internal pipe, and a heating portion comprised of a resistance heating coil which is installed between the fusing portion and the internal pipe and generates heat. In order to compensate for the roll off in temperatures near the ends of the fusing roller, the resistive heating element near the end portions of the fusing roller are spaced closer together than at the center of the fusing roller.